The present invention is concerned with measuring instruments containing analog display means, such as having an indicator move along a graduated scale. More particularly, the invention is concerned with a viewing glass which renders the measurement more visible.
Conventional measuring instruments mostly contain an inorganic glass window, usually plane or slightly curved, of uniform clarity which is mounted in front of the display means. Furthermore, in most industrial measurements there is a need to verify whether or not the measurement is in predetermined tolerances. Thus, it would be convenient to furnish the display means with means to affix a marker which is movable and is capable of being adjusted from outside of the instrument to enable the minimum and maximum limits of the tolerance range to be easily observed.
Some instruments, such as those used for the measurement of lengths achieve this object by using two display needles to be placed to indicate the limits. This approach has problems because of high costs and because the marking needles have to be mounted with great care in the viewing glass in order to accurately remain where they have been placed. Additionally, since the position of marking needles are frictionally moved, such mechanism deteriorates with time.